The advent of low cost microprocessors and microcomputers for use in "intelligent" data terminals, and the lower costs and improved efficiency of computer systems in general have resulted in ever-increasing numbers of applications for unattended credit operations, such as automatic bank "tellers", unattended bulk terminal fuel dispensing systems, and the like. Such systems usually are operated in response to the entry of an authorized credit card having variable data encoded on it to identify the user, the types of products, or extent of credit to which the user is entitled, and other information required by the particular system with which the card is used. Usually, the credit card or authorization card is inserted into a card reader. Then, the variable data relative to the specific transaction desired by the user is entered by means of a keyboard or other actuating device to cause the system to perform the desired operation.
A typical system with which such a card reader is used is the automatic product dispensing system disclosed in U.S. Pat. No. 4,085,313 issued Apr. 18, 1978. The system disclosed in this patent is a fully automatic self-service fuel dispensing system in which the transactions are controlled by the insertion of a credit card or identification card document into a card reader. Selected data from the card, as supplied by the card reader, is combined with the variable information relative to the transaction for further processing by the computer system which is utilized to control the operation of the fuel-dispensing devices and to compile and prepare the necessary billing information for the completed transaction at the fueling site.
The credit cards or transaction control document cards which are used in the readers may be encoded in a variety of ways. Typically, encoding has been accomplished in the past by physically punching holes through the cards for utilization with a photoelectric reader. Other systems use magnetically encoded spots in which the data on the card is encoded by means of permanently magnetized slugs or magnetic material laminated between outer layers of the card. Other encoding is accomplished by means of magnetic strips placed on the card and pre-magnetized with the unique data used to identify that card and provide other necessary information for the operation of the system with which it is used.
To ensure that the data supplied by the card to the computer system for effecting the desired transaction is correctly read by the reader and utilized by the system, most readers have a mechanical or quasi-mechanical sensor located in them. This sensor produces a signal which is utilized by the remainder of the system to indicate that the card has been fully inserted into the reader in a proper reading position. Frequently, this is done by locating a columnated light source and a light-sensing diode in the reader in a position where a fully inserted card breaks the column of light between the light source and light-sensing diode. Whenever this occurs, the information is used by the computer and data processing system to indicate that the card is in place; and the transaction continues either to initiate reading the data on the card or to utilize information previously read from the card and stored in a buffer memory for release when the light column has been broken. When the card is withdrawn from the reader, the light source once again causes light to impinge upon the light-sensing diode and a signal indicative of this is obtained from the diode. Subsequent signals then may be used to terminate the transaction and to reset all of the various circuitry operated in conjunction with the reader to prepare the system for a new transaction initiated by the insertion of another card into the reader.
Problems exist in the use of a light source and a light-sensing diode, however, since the environment in which the reader is located frequently is subject to a number of conditions which may interfere with the brilliancy of the light path. For example, readers often are located out-of-doors, and dust and other contaminants may enter the reader and build up on the light-sensing circuitry. In addition, aging of the light source or burning out of the bulb, or even use of different materials for the cards used in the system, can result in faulty operation. This then requires maintenance or other adjustments which are in addition to any which the computer system and the card reader system itself would otherwise require.
Another approach has been to provide a micro-switch which is engaged by the edge of the card to provide a similar "card in place" output signal for utilization by the system. Mechanical micro-switches are subject to many of the same disadvantages encountered with the photoelectric system described above. Switch failures occur, the switches tend to stick as a result of contaminants entering the card slot, and the switch also is an additional initial expense in the construction of the reader.
To overcome the disadvantages of these mechanical or quasi-mechanical systems, other attempts for sensing the presence or movement of a card in a card reader have been made. A system which uses a Hall-effect transducer to operate logic for verifying the presence of a card is disclosed in the Patent to May, U.S. Pat. No. 3,896,292, issued July 22, 1975. This system employs a card with a high permeability metal insert in it. The insert is placed to overlie a detecting transducer when the card is in the "read" position in the reader. Whenever the card is moved away from this position, the transducer provides a signal to reset the system logic. While the sensing transducer is not subject to the mechanical failures possible with the photoelectric and micro-switch sensors described above, it requires a specially constructed laminated card in order for it to function. The data sensing in the reader is effected by different circuitry from the circuitry used to sense the card presence.
Two other patents which disclose separate sensors for sensing premature card withdrawal are the patents to Oldenkamp, U.S. Pat. No. 4,322,613, issued Mar. 30, 1982 (using a mechanical sensor), and Cannon, U.S. Pat. No. 4,058,705, issued Nov. 15, 1977. In Cannon, a magnetic card reader is disclosed with a self-balancing nulling circuit. The circuit uses a delay and a comparator to continuously set a reference level for accurate reading of the data from the card, but there is nothing in this system to act as a "card removed" sensor as well as a data reader.
It is desirable to provide a system for controlling the transaction by means of a card inserted into a card reader which does not require separate "card in place" or "card removed" sensors to provide such information.